10.3.1: Common Pathogens

Bacteria are single-celled microorganisms that can be found virtually everywhere on Earth. Common bacterial pathogens include the following:

• Streptococcus: Responsible for various infections, including strep throat and skin infections.
• Escherichia coli (E. coli): Some strains can cause food poisoning and urinary tract infections.
• Salmonella: Often associated with foodborne illnesses.
• Mycobacterium tuberculosis: The causative agent of tuberculosis (TB).
• Staphylococcus aureus: Can cause skin infections, pneumonia, and more, including Methicillin-resistant Staphylococcus aureus (MRSA).

Viruses are much smaller than bacteria and contain genetic material (DNA or RNA) enclosed in a protein coat. They require a host cell to reproduce. Common viral pathogens include

• Influenza virus: Responsible for seasonal flu outbreaks.
• Human immunodeficiency virus (HIV): The virus that leads to acquired immunodeficiency syndrome (AIDS).
• Herpes simplex virus: Causes oral and genital herpes.
• Human papillomavirus (HPV): Linked to various types of cancer and genital warts.
• Hepatitis viruses (A, B, C): Cause liver inflammation and can lead to chronic liver disease.

Fungi are eukaryotic (made of more than one cell) microorganisms; some species can cause infections in humans and animals. Common fungal pathogens include

• Candida albicans: Responsible for yeast infections in the mouth, throat, and genital area.
• Aspergillus: Can cause lung infections, especially in individuals with weakened immune systems.
• Cryptococcus: Affecting the lungs and central nervous system, especially in individuals with compromised immunity.
• Dermatophytes: Responsible for various skin infections such as athlete's foot and ringworm.

Protozoa are single-celled eukaryotic organisms that can cause various diseases, especially in tropical and subtropical regions. Common protozoal pathogens include

• Plasmodium: Responsible for malaria, a widespread and deadly disease.
• Entamoeba histolytica: Causes amoebic dysentery.
• Giardia lamblia: Causes giardiasis, a gastrointestinal infection.
• Trypanosoma: Causes diseases like African sleeping sickness and Chagas disease.

Parasitic worms are multicellular organisms that can infect various parts of the body. Common helminthic pathogens include

• Ascaris lumbricoides: Causes intestinal roundworm infections.
• Schistosoma: Responsible for schistosomiasis, a tropical disease affecting the urinary and intestinal systems.
• Taenia saginata and Taenia solium: Tapeworms responsible for intestinal infections.

(Janeway et al., 2001)

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